The invention relates to apparatus for pressure testing tubing.
Apparatus of this type is known from U.S. Pat. No. 1,637,956. This apparatus, however, is only useful for pressure testing rigid tubing because the ends of the tubing are supported and sealed by two spigots or support members urged together axially, the spigot forming a stationary tube support having an inlet duct for the test medium. This known apparatus is not suitable for testing flexible tubing, because it cannot seal the test medium into the test piece. Moreover, an actuating spindle in the known apparatus is the sole drive for the movable support member. If the metal-to-metal contact line between the conical end of the spigot and the tube is to be adequately sealed, extraordinarily high forces must be used to lead to a small plastic deformation of the edge of the tubing. If the seal is broken during the test, the test medium escapes at high pressure and there is a substantial risk to the person carrying out the test.
German Patent Specification No. 440,669 describes two different test devices which, like the above described apparatus, can only be used for rigid tubes. Moreover, they test the tubes only for their lengthwise strength and this necessarily precludes compressing the tubes by driving in a conical spigot. In one device, only tubes with flanges at each end can be tested, the sealing being effected at each end by a hydraulic piston. There is a rack and pinion, but this has no self-adjusting action and is not connected in tandem with the hydraulic drive serving only for the adjustment, off load, of one piston. In the other device, one of the hydraulic pistons is not required and it is retracted by the rack and pinion. In both cases, test medium is led into the tubing from the end remote from the mechanical adjustment device and this also excludes the testing of flexible tubes.
Test pressures are often greater than 1000 bar and thus the main problem is usually that of locating and sealing the test piece. There are many different variables to be accommodated--there are differences in nominal bore, types of connector, length of the test piece, forms of the two ends of the tube, and so on. Alone, the connector can have further variations, such as metric or imperial thread, external or internal thread, sloppy and tight tolerances in bore size, angled fittings with bends of 30.degree., 45.degree., 60.degree., 90.degree., and so on. The possible variations are further augmented by the option of screw fittings and press fittings. The two systems have different external dimensions. If you multiply all the variables, you get a theoretic number of 10.sup.6 types.
With such a multiplicity, the task of connecting a tube for a pressure test is extraordinarily costly, not only because you have to have a whole range of adapters for the two ends of the tube but also because of the time taken to set up the test.
For example, you might have to thread a complementary adapter to a metal connector before carrying out the test. This means, however, that you have to have a suitable adapter for each type of connector likely to be submitted for test.
It is also known to seal connectors by means of a ring that cuts into them with an encircling nut. This, however, is not possible for a large number of fittings, such as so-called tube-reinforcing fittings.
It is furthermore known, for pressure testing, to insert a spigot into the bore of the connector and seal it by means of washers. The wear on the washers is substantial, however, and moreover, the bore tolerances are usually so sloppy that the washers cannot fill the gaps. The washer is thus frequently pressed into the space between the spigot and the bore and the seal is broken at high pressure.